The overall objective of this proposal is to investigate the role of the androgen receptor (AR) in prostate cancer metastasis. Prostate cancer is the second leading cause of cancer-related death among men in the United States. Androgen action and the functional status of the AR are believed to be the important mediators of prostate cancer development. Although androgen/AR is known to promote growth of androgen-dependent prostate tumors, its function in tumor metastasis is unclear at present. A preliminary study has been made in Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) mouse models of prostate cancer and discovered that ablation of the AR in prostate epithelium resulted in development of larger pelvic lymph node (PLN) metastatic tumors and higher numbers of liver metastatic foci, suggesting that AR might function as a suppressor of prostate tumor metastasis. Therefore, the proposed studies will use various ARKO models of TRAMP mice and human prostate cancer cell lines with different AR expression to investigate the suppressor role of AR in prostate tumor metastasis. Initially prostate epithelium-specific (pes) AR knockout (ARKO) (Aim 1) and inducible ARKO TRAMP mice (Aim 2) will be generated to study the effect of pes-ARKO and induction of ARKO, after prostate tumors have developed, on PLN metastatic tumor formation and growth as well as the expression levels of various metastasis-related genes. Subsequently, the effect of suppressing AR expression (with AR-specific RNA interference) in AR-positive and restoring AR expression (with functional AR cDNA) in AR-negative PLN tumor cells and various human prostate cancer cell lines (Aim 3) on their invasive properties and expression levels of metastasis-related genes will be studied in vitro as well as in bone xenografts in SCID mice. Finally, the molecular mechanisms through which AR regulates the expression levels of various metastasis-related genes will be studied (Aim 4). Therefore, the success of this application undoubtedly will uncover an alterative role of the AR as a metastasis suppressor during prostate cancer progression. The establishment of the AR function as a metastasis suppressor and understanding of how it regulates tumor metastasis-related genes, should lead to new concepts of treatment modality and molecular targeting for prostate cancer therapy. Project Narrative: Loss of Androgen Receptor Promotes Metastatic Cancer. We will study the loss of androgen receptor in prostate epithelium and the influence of this loss on prostatic metastatic tumor invasion. The success of this application undoubtedly will uncover an alterative role of the androgen receptor as a metastasis suppressor during prostate cancer progression. The establishment of the androgen receptor function as a metastasis suppressor and understanding of how it regulates tumor metastasis-related genes, should lead to new concepts of treatments and molecular targets for prostate cancer therapy.